The present invention relates to low temperature curable organic resin compositions based on the use of a diaryliodonium salt, a copper salt and a reducing agent, for example, ascorbic acid, an Sn.sup.+2 compound, an activated .alpha.-hydroxy compound, etc. More particularly, the present invention relates to low temperature curable compositions useful in reaction injection molding applications.
As shown in my copending application Ser. No. 962,997, filed Nov. 22, 1978 and assigned to the same assignee as the present invention, aromatic iodonium salts can be employed in combination with organic acids or copper salts to facilitate the heat cure of various organic materials, such as epoxy resins. I have also found, as shown in my copending application Ser. No. 940,564, filed Sept. 8, 1978 and assigned to the same assignee as the present invention, that valuable results also can be achieved if reducing agents, such as thiophenol are used in combination with aryl onium salts to facilitate the thermal cure of epoxy resins. Surprisingly, in the absence of such cocatalysts, the cure of cationically polymerizable organic materials, such as epoxy resins, with an aromatic iodonium salt can require temperatures exceeding 200.degree. C. over an extended period of time. I have now discovered that if a diaryliodonium salt of the formula, EQU [(R).sub.a (R.sup.1).sub.b I].sup.+ [Y].sup.- ( 1),
is employed with a catalyst comprising a mixture of copper salt, and a reducing agent defined more particularly hereinafter, the cure of a cationically polymerizable organic material, for example, an epoxy resin can be achieved spontaneously, or in a few minutes or less without the use of external heat, or initiated at a relatively low temperature, where R is a monovalent aromatic organic radical, R.sup.1 is a divalent aromatic organic radical, Y is a non-nucleophilic anion defined below, a is a whole number equal to 0 or 2, b is a whole number equal to 0 or 1, and when a is 0, b is 1, and when b is 0, a is 2. A possible cure mechanism is that a strong protonic acid is released based on the spontaneous breakdown of the diaryliodonium salt.